A conventional scroll compressor (hereinafter abbreviated as compressor) comprises, as shown in FIG. 4, a rear casing 32 having an opening at the front side, and a front cover 31 placed in its opening. A movable scroll 34, a fixed scroll 39, and a rotation preventive mechanism 36 are disposed in the rear casing 32. An outer circumference of the fixed scroll 39 contacts with an inner circumference of the rear casing 32. The movable scroll 34 is placed between the front cover 31 and the fixed scroll 39 in order to swivel while contacting with the surface of the fixed scroll 39. The rotation preventive mechanism 36 is placed between the movable scroll 34 and the front cover 31 in order to allow the swivel motion only while preventing rotation of the movable scroll 34. A suction chamber 46 for sucking a refrigerant and a discharge chamber 47 for discharging the refrigerant are mutually partitioned through the fixed scroll 39. A suction port 32c for sucking the refrigerant is formed in an outer wall of the rear casing 32 of the suction chamber 46. A discharge port 32d for discharging the refrigerant is formed in the outer wall of the rear casing 32 of the discharge chamber 47. A seal mechanism having an O-ring 41 is placed between the inner circumference 32a of the rear casing 32 and the fixed scroll 39. This seal mechanism seals between the fixed scroll 39 and the rear casing 32. It is thus completely sealed between the suction chamber 46 and discharge chamber 47. A plurality of mounting bases 32b for mounting on a vehicle or other mechanical structure are integrally disposed on the outer wall of the rear casing 32. The front cover 31 has a clutch mounting section 31c. A shaft 40 is installed so as to cooperate with the movable scroll 34, and this shaft 40 penetrates through the clutch mounting section 31c, and has its leading end exposed outside. An electromagnetic clutch 38 is installed outside of the clutch mounting section 31c, and is coupled to the shaft 40. The front cover 31 is coupled to the rear casing 32 through a seal member 45, by using bolt 44 or other bonding member. The seal member 45 seals between the front cover 31 and rear casing 32, and by this seal member 45, the suction chamber 46 and the outside are completely isolated. Thus, a pressure vessel sealing between the suction pressure and atmospheric pressure was constituted.
Generally, when mounting a compressor of an air compressor on a vehicle, it is required to be high in the precision of pitch of the plurality of the mounting bases 32b of the compressor main body, precision of alignment of electromagnetic clutch, precision of discharge port and suction port pitch, and precision between these adjacent elements. In such conventional compressor, however, the front cover 31 having the mounting section 31c for the electromagnetic clutch 38 is composed of a separate part from the rear casing 32 having the plurality of mounting bases 32b, suction port 32c and discharge port 32d. Accordingly, the both parts of the front cover 31 and rear casing 32 must be heightened in the precision, including the machining tolerance in both axial direction and rotating direction and tolerance in assembling. The invention presents a compressor easily matched with the requirements of the vehicle to be used.